1. Field of the Invention
The present invention relates to ink jet printing devices, and more particularly, to recording apparatus which utilize a plurality of streams of droplets which are controlled to print on a printing medium.
2. Prior Art
The present system is especially suited for use in prior art devices of the general type disclosed for example, in U.S. Pat. Nos. 3,701,476 and 3,739,393. Such ink jet printing devices generate series of droplets from a plurality of orifices disposed in a row or rows and formed in a manifold or printing head so as to produce an array extending laterally over a recording medium or surface and expell drops of ink or other liquid toward the surface. The systems are stimulated at a common predetermined frequency so that uniform filament lengths and droplets are generated from each orifice in a fixed phase relationship with the stimulating source.
In such devices, the drops travel toward the recording surface and are selectively charged in binary fashion according to intelligence signals from a computer or input source. The drops to be excluded or caught are electrostatically charged and then passed through a constant electrostatic deflection field which deflects them from their initial trajectory into catchers, while uncharged drops are deposited on the recording medium since they are unaffected by the deflection field and follow their initial trajectory onto the receiving surface.
In order for such systems to operate properly, a high degree of accuracy of uniformity in drop generation is important since the inability to maintain the proper phase relationship between the stimulating source and the drop generation results in the improper charging of droplets so that control over those droplets which are not supposed to contact the recording surface can be lost thus reducing the clarity of the intended print configuration.
Many different means have been devised for controlled stimulation of filament and droplet formation, such as those utilized in the above referred to patents. For example, these systems utilize a mechanical stimulator which extends through the fluid supply reservoir and vibrates the orifice plate so as to cause a traveling wave of vibrations along the length of the orifice plate. This causes generation of filaments of a particular length and uniform formation of droplets at the ends of the filaments with adjacent orifices producing droplets in predictable phased relationship to one another so that adequate control of drop charging and catching can be maintained. However, since the drop generation along the row of orifices is cyclical due to the use of traveling wave technique to produce the series of uniform droplets, complicated computer switching techniques must be utilized to account for the phase shifting so that charging and deflection of the desired droplets is obtained.
It is therefore more advantageous to utilize a drop generation stimulation system which causes simultaneous stimulation of all of the orifices along an orifice plate. Attempts have been made to accomplish this by various techniques such as that disclosed for example in French Pat. No. 2,999,093, in which the orifice plate along with the reservoir of printing fluid is vibrated by magnetic attraction to a magnetically activated portion of the orifice plate and reservoir with an attractive electromagnet being stimulated at the desired frequency of vibration to produce the uniform series of droplets from the orifices. Such a device, however, is relatively massive since the orifice plate and manifold containing the reservoir and also the fluid, must be vibrated up and down at high frequencies.
Another method devised in the prior art for causing uniform stimulation of drop generation from a plurality of orifices and which also employs magnetic attraction as its motive force, involves the use of the magnetostrictive characteristics of many materials. In essence, a magnetic field is established which passes through the magnetostrictive material and causes expansion or contraction of the material which is placed either adjacent the orifice or is somehow in contact with the fluid to cause the fluid to be expelled through the orifice upon excitation of the magnetic field. Such devices are disclosed, for example, in U.S. Pat. Nos. 4,057,807 and 3,679,132.
However, these proposed structures are not particularly suited for producing uniform generation of droplets from long rows of orifices simultaneously and therefore require reliance on activating the magnetic field sources simultaneously which results in difficulties similar to those encountered with traveling wave stimulation techniques which results in lack of uniformity in the magnetic field and force applied to the liquid due to variations in the parts of the assemblies.
Still further devices have been proposed which actually use a magnetostrictive device coupled to the orifice nozzles to move the nozzles either in the plane of drop generation or perpendicular thereto, such as for example, those devices disclosed in U.S. Pat. Nos. 3,287,734 and 3,737,914. However, these devices would necessarily be operated at relatively low frequencies due to the mass required to be moved and would thus substantially restrict the speeds at which ink jet printing could be obtained.